Master-control clock



NOV. 14, 1950 FREDSTRQM 2,529,869

MASTER-CONTROL CLOCK Filed Nov. 9, 1948 Patented Nov. 14, 1950 UNITED STATES PATENT OFFICE MASTER-CONTROL CLOCK Gustave TJ'Fredstrom, Chicago, 111.

Application November 9, 1948, Serial No. 59,076

.'5 Claims. (CI. 58-25 This invention relates to automatic time-control systems in which a master clock is caused to supply electrical impulses for the operation and correction of one or more slave clocks. In particular, it concerns a new and improved master clock.

Master-slave clock systems of the type here under consideration are widely used wherever it is necessary that a number of clocks be consistently in step with one another. Thus such systems are generally used in factories, to .maintainall cardstamping clocks and automatic bells in identical time-step; similarly, such systems are used in schools to keep the clocks in each classroom at all times indicating the same time. Many other applications for systems of this sort could be enumerated.

A highly desirable feature of such systems is an automatic correction apparatus which periodically causes each of the slave clocks to be brought into agreement with the master clock in the event that a failure of electrical current or other mishap has caused one of the slave clocks to :fall out of step.

In prior-art systems, the master clock has normally been a pendulum-type clock, actuated byLa spring or by weights. Such a clock can be .designed to give a high order of accuracy over :a long period of time, but when so designedis normally very expensive. In prior-art systems, the control of the slave clocks has been accomplished by electrical impulses produced by the periodic operation of switches which, in turn, have been operated by cams carried on the hour, minute,

and second-hand shafts of the master clock. One

serious limitation of prior-art systems has been that hand-re-setting of the master clock had'to be undertaken with great care and by a highly skilled operator, in order to avoid shifting of the relative positions of the hour, minute, and secand-hand shafts.

In the present invention, alternating current from the commercial power circuits is employed to actuate the master clock, and accordingly the system can be made as accurate in all respects as the timing system employed by the power company for holding the frequency of its current at a standard value, All power companies today maintain their standard frequency with zero error over a period of time, and with only a very tiny error at any given instant. It is, accordingly, a better time standard than could normally 'be provided in a system using a pendulum-type master clock.

An object of this invention is toprovide a master-clock structure which can be operated from--a commercial power source without the necessity for periodic winding or regulation.

Another object of this invention is to provide an electrically-operated master clock in which time-setting adjustments can be made rapidly by an unskilled operator without any possibility of the minute andsecond mechanisms being de-synchronized.

A further object of this invention is to provide, in a simple, inexpensive construction, a master clock which will maintain time accuracy :and keep a plurality of slave clocks on time. A still further object of this invention is to provide :a system of gearing and switching in a masterclock which insuresagainst .de-synchronization of the various timing and correction impulses sent :to the slave clocks.

A still further object of this invention is to provide, in an electrically-powered master clock, a manual means by which the slave .clocks can be moved rapidly to a desired setting and thenlree turned to the automatic control of the master clock.

Still another object of my invention is to pro-. vide a gearing mechanism for a master clock in which the setting of the master clock'can ,be varied manually to any desired readingwithout in any Way disturbing the normal functioning of the driving mechanism or de-synchronizing the various impulse-generating elements.

Other objects .and advantages of my invention will appear as the specification proceeds.

The invention is illustrated, .in a preferred em-i bodiment, in the accompanyingdrawing, of which Figure l is a. plan view of the chassis of a master clock madeaccording to my invention; Fig. 2. is a view of .the 'sam'e chassis in front elevation; Fig. 3 is a view of the-same structure inrear elevationy-and Fig. 4fis a schematic diagram show ing the electrical wiring within the master clock and the manner in which it is to be connected to the slave clocks. Referring to the drawing, the master-clock apparatus is mounted onla chassis comprising a front plate 1.0,aback plate I I, and a plurality of suitable spacers l3. .Bolts [4 pass through the respective plates andhspacers andareanchoredin place by nuts I15.

On backiplate H a synchronous motor 16 is mounted, with its output gear is! protruding backward through a suitable aperture in plate ll. Synchronous motor l6 maybe of any type" appropriate to the voltage and frequency of the available current. a-Normally such motors are supplied with built-in step-down gear trains which give a relatively low rotational speed to the output shaft. In the embodiment illustrated, the output gear I! normally turns at a speed of 10 R. P. M., and the associated gearing in my invention is designed accordingly. It will be understood that any synchronous motor speed may be used with appropriate modification of the gearing. ,Gear I1 meshes with a large gear I8 which has ten times'as many teeth as gear I'l, so that as gear Isis turned by gear I'I its speed is one-tenth that of gear lI-namely, one revolution per minute.

Gear I8 is carried on a shaft I but is adapted to turn freely thereon. At a suitable point on its outer face, gear I8 carries a ratchet 20 which is spring-biased by a spring 20a, as shownbest in Fig. 3. Ratchet 20 bears against a ratchet gear I9 which is mounted on shaft I00 adjacent gear I8. Ratchet gear-*l9 is rigidly aflixed to shaft I00. To the rear of ratchet gear I9 on shaft I00 are two cams, each of which is rigidly affixed to shaft I00. These cams, denoted respectively 2| and 22, are formed of an insulating material and are used to operate electrical switches 24 and 23 respectively.

Shaft I00 is carried in suitable hearings in the plates I0 and II respectively, and on the shaft, between the said plates, a small gear 25 is carried, rigidly affixed to the shaft. An idler shaft IOI is carried in suitable bearings in the plates I0 and II, and a gear 26 is rigidly affixed to shaft IOI at a position at which it meshes with gear 25 on shaft I00.

A small gear 21 is likewise carried on shaft IOI; it meshes with a large gear 28 which is rigidly afiixed to a shaft I02, which is also supported by the end plates I0 and Il. Shaft-IOI is extended through plate I 0 forwardly and is terminated by a manual adjustment knob 29.

The total step-down ratio achieved by the gear train comprising gears 25, 26, 21, and 28'is 60 to 1, so that the rotational speed of shaft I02, when driven by synchronous motor I6, is one revolution per hour. I

'Shaft 102 is extended through plate ID in forward'direction and carries, in front of plate I0, a'r'pointer 35 and-two cams, denoted 30 and 3I respectively. For convenience in adjustment, the cams 30 and 3I' are, in the illustrated embodiment, comprised of two leaves each. Thus, by varying the relative positions of the leaves on the shaft, the angular width of the recess or lowered portion on each cam can be adjusted at will. Pre-cut cams employing a single leaf may, if desired, be used insteadof the two-leaf cams illustrated.

; Cams 30 and 3| are employed to actuate electrical switches 32 and 33 respectively.

1 Of the cam-operated switches illustrated,

, duced-radius portion ofv cam 3|, contacts X and Y are opened and contacts Y and Z are closed. @Cams ZI-and 22 are carried on the '1 R. P.-'M. shaft I00; a reduced portion ofzcam 2| 'isicut Switch 33, on the other hand, is a single-' to occupy an arc of 12 degrees, while the reduced-radius portion of cam 22 may be cut to occupy any desired arc. Normally, the reduced portion of cam 22 will occupy an arc of from 36 degrees to 60 degrees. Cams 2I and 22 are placed on the shaft I00 at positions such that when the shaft is being driven by synchronous motor I6 cam 2I causes switch 24 to close from the 58th to the 60th seconds of each minute, while cam '22 causes switch 23 to close at'the first second of each minute. The length of time switch 23 remains closed depends, of course, on the are occupied by the reduced portion of cam 22.

Cams 30 and 3| are carried on the l R. P. H. shaft I02. Cam 30 is provided with a reduced portion occupying an arc of 3 degrees, and it is placed on shaft I02 in such a position that switch 32 is closed once each hour from 59 15 to 59' 45". Cam 3I is provided with a reduced portion occupying an arc of 61 degrees, and it is positioned on shaft I02 such that contacts X and Y'of switch 33 are opened each hour at 49' 30" past the hour and remain open until 59 45" past the hour.

A motor-operated switch 38, which will open and close intermittently, is shown diagrammatically as element 38 on Fig. I. A motor for the operation of switch 38 is shown as element3l. Switch 38 may be a micro-switch operated by a rotating cam, or any other type of similar device which will produce, when motor driven, an intermittently-closed circuit. The speed of operation of switch 38 is a matter of choice; I prefer to face broken away to reveal, diagrammatically, its

internal structure. Each slave clock-comprises an escapement mechanism which operates the hands and which is in turn actuated by an elec tromagnet. The electromagnet comprises a pair of coils, denoted Mb and Mo respectively; Each time an electrical impulse passes through either of the coils, the escapement mechanism is actuated and theclock hands are caused to advance One terminalof coil M0" is connected to-line B, the otherto'line C. One terminal of coil Mb is connectedto line C; 'the other one minute.

is connected through switch Md to line A.-

SWitch' Md is a single-pole single-throw; nor; mally-closed switch which is'cam-operatedby cam Ma, carried on the minute-hand shaftof-the' slave clock; Normally both electrodes of switch Md press against cam Ma andare'in contact with one another. The upper leaf of switch Md drops off the raised portion ofcam Ma two minutes before the lower leaf is released by the cam; however, and as a result switch Md is open fortwo minutes during each hour. Cam Ma is placedon the minute-hand shaft in such position that the switch Md opens at the 59th minute of each hour and closes atthe first minute of the succeeding hour.

Referring to-Fig; 4, apower-line denoted Line isshown, including terminals 60 and 6h Syn-'3 chronous motor I6 is connecteddirectly across? terminals-60 and 6|. Terminal 60"is connected through switch 24 to one side of the coil of relay 40; the other:side or the coilof'rel'ay lfl is cohnected to line terminal 6|. Line terminal 60 is connected to contact F of switch32, while contact E of switch 32 is connected to one side of motor 31. The other side of motor 31 isconnected to line terminal 3 I. Contact E of switch 32 is also connected to one terminal of switch 38; the other terminal of switch 38 is connected to one side of the coil of relay 39. The other side of the coil of relay 39 is connected to line terminal 6|.

A manually-controlled switch 3% is connected across the terminals of cam-operated switch 32. The contacts of relays 39 and 40 are connected in parallel; one set of contacts is connected to line terminal 6| while the other set of contacts runs to line C of the cable to the slave clocks.

Contacts Y and Y of'switch 33 are connected to line terminal 30. Contact X of switch 33 is connected to line B of the cable to the slave clocks, while contact Z of switch 33 i connected to line A of the cable to the slave clocks. The contacts of switch 23 are shown in Fig. 4 as connected to signal circuit. The function of this switch and its associated cam is to provide a signal of predetermined duration to govern the operation of bells, lights, or other signal devices which are to be automatically actuated by the master clock.

Operation In the operation of my invention, th master clock can first be set to the correct time by operation of manual adjustment knob 29. Gear l8 turns freely on shaft 180; the manual knob 29 will easily turn the various gears in the train, since it does not have to force the revolution of gear [8 or of synchronous motor [6. Ratchet 20, however, prevents the manual knob 29 from being turned backwards, since any attempt at backward rotation causes ratchet 20 to engage ratchet gear l9, and the torque required to turn the entire system, including gears l8 and I1 and motor I6, is so great that manual rotation of knob 29 in the reverse direction is not possible. When the master clock has been set to the correct time, motor [6 may be started and-the system will thereupon proceed to function automatically, shaft I00 turning at one revolution per minute and shaft )2 turning at one revolution per hour. Qnce each minute, as cam 21 causes switch 26 to close, relay 40 closes for two second and an electrical impulse is transmitted to the slave clocks on wires B and C. This causes each of the slave clocks to advance one minute. This procedure is repeated until the master clock reaches 49 30 after the hour. At this time cam 3| causes switch 33 to shift its position, contacts X and Y Opening and contacts Z and Y closing. Thereafter, for the next ten minutes, the impulses produced by cam 2| and switch 24 are transmitted to the slave clocks on wires A and C. When the hands on any given slave clock reach 59' after the hour, the cam-operated switch within the clock i opened and the circuit through wires A and C is broken. At 59 and 45" after the hour switch 33 is caused to resume its normal position; contacts Y and Z open, contacts X and Y close, and the minute-impulses are again transmitted through wires B and C to the slave clocks.

Meanwhile, at 59 minutes and 15 seconds after the hour, cam 30 causes switch 32 to close, which starts motor 31. Thereupon switch 38 begins closing and opening intermittently at a relatively rapid rate-preferably about 60 to 70 times per minute. This causes impulses to be transmitted to the slave clocks on wires A and C. Any slave clock which is on time does riotrresp'ond to these impulses, since its A-C circuit will have been broken at the 59th minute by the opening of its cam-operated switch. If the clock is slow, however, theswitch will not yet have opened and the rapid impulses will cause a rapid advancement of the hands of such clock until its hands reach'the 59th minute. At that time, the cam-operated switch in the slave clock will open and the clock will respond no longer to the correction-impulses being transmitted over the wires A and C. At the 60th minute, as has already been mentioned, the minute-impulse comes over the B-C circuit and the clock responds normally, since that'circuit is not affected by cam-operated switch Mb.

It will be seen by study of the foregoing that a given slave clock will be corrected at each hour, provided it is no more than ten minutes 'fastor fifteen to twenty minutes slow at the time its hands reach the 59th minute position.

Should the system have been inoperative for some time, or should the slave clocks be badly off schedule by reason of a power failure or other mishap, the correction-impulses can be started at any time by closing manual switch 36. This starts motor 31, irrespective of the position of cam 30, and causes correction-impulses to be transmitted over wires A and C continuously so long as switch 36 is closed. To put the system back into adjustment, it is merely necessary that switch 36 be used to place the slave clocks in approximate step with the master clock-'say within 5 or 6 minutes'in either direction-and" the system will automatically place all the slave clocks on exact time at the beginning of the next hour.

It will be understood that switch 23 and cam- 22 do not normally provide sole control of an outside signal, such as a bell or light. Those elements merely control the duration of the signal-impulse, and normally the determination as to whenthe signal-impulse Will be transmitted to the honor light will be controlled by a separate switch oper atedby a cam on the l R. P. H. shaft.

The number of minutes correction which can be supplied to slow slave clocks at any given hour is determined, as may be seen, by theratefl at which correction-impulses, are transmitted by motor-driven switch 38. In practice, switch 38 can be made to operate much more rapidly, how ever, than the magnetic escapement mechanisms in the slave clocks can follow it. Accordingly, the practical upper limit of operating speed of switch 38 is about'lO to '75 impulses per minute.

It will be understood that the duration of the correction intervals, and the consequent proportioning of the cams in the system, may be varied at will. In the operative system which I have described, I have chosen correction intervals which are convenient and which meet practical requirements. My invention, however, is not limited to any particular intervals for correction or to any particular intervals for the transmission of control impulses. Obviously, a shaft of suitable speed could be provided to cause switch 24 to transmit one impulse per second, one impulse every five minutes, or such other arrangement as might be convenient.

The relays 39 and 40 are provided merely to permit switches 24 and 38 to break light currents; in a system with a large number of slave clocks, the total load current, broken by the relays 39 and 40, may be quite large. In a case where the load current is not greater than can safely be handled by the switches 24 and 38, switch 24 may be connected :in the position of the contact points of relay 4B and switch 38 may be placed directly in shunt with switch 24. This will eliminate relays 39 and 40 from the circuit.

While I have in'this specification described a particular embodiment of my invention in considerable detail for purposes of illustration, it will be understood that many variations may be made thereon by persons skilled in the art without departing from the spirit of my invention.

vI claim:

1. In a master clock for transmitting control and correction impulses to a slave clock, a shaft, a ratchet gear rigidly affixed thereto, a driving gear freely rotatable on said shaft, a ratchet carried by the driving gear adapted to engage the ratchet gear, power means for turning the driving gear at one revolution per minute, a second shaft, a gear train coupling the shafts operative to turn the second shaft at one revolution per hour, a cam on each shaft, a switch adapted for intermittent actuation by the cam on the first shaft, and a double-throw switch adapted for intermittent actuation by the cam on the second shaft.

2. In a master clock for transmitting control and correction impulses to a slave clock, a shaft, a ratchet gear rigidly afiixed thereto, a driving gear freely rotatable on said shaft, a ratchet carried by the driving gear adapted'to engage the ratchet gear, power means for turning the driving gear at one revolution per minute, a second shaft, a gear train coupling the shafts operative to turn the second shaft at one revolution per hour, a camon each shaft, a first switch adapted for intermittent actuation by the cam on the first shaft, a second switch adapted for intermittent actuation by the cam on the second shaft, and means operative on actuation of the second switch to short-circuit the first switch intermittently at a substantially more rapid rate than the first switch is normally actuated by the cam on the first shaft.

3. In a master clock for transmitting control and correction impulses to a slave clock, a shaft, a ratchet gear rigidly aifixed thereto, a driving gear freely rotatable on said shaft, a ratchet carried by the driving gear adapted to engage the ratchet gear, power means for turning the driving gear at one revolution per minute, a second shaft, a gear train coupling the shafts operative to turn the second shaft at one revolution per hour, a cam on each shaft, a first switch adapted for intermittent actuation by the cam on the first. shaft, a second switch adapted for intermittent actuation by the cam on the second shaft, means operative on actuation of the second switch to short-circuit the first switch intermittently at a substantially more rapid rate than the first switch is normally actuated by the cam on the first shaft, and a manually-operable switch connected in shunt with said second switch.

4. In a master clock for transmitting control and correction impulses to a slave clock, a shaft, a ratchet gear rigidly affixed thereto, a driving gear freely rotatable on said shaft, a ratchet carried by the driving gear adapted to engage the ratchet gear, power means for turning the driving gear, a second shaft, 2. gear train coupling the shafts operative to turn the second shaft at a slower rate of revolution than the first shaft, a cam on each shaft, a switch adapted for intermittent actuation by the cam on the first shaft, and a double-throw switch adapted for intermittent actuation by the cam on the second shaft.

5. In a master clock for transmitting control and correction impulses to a slave clock, a shaft, a ratchet gear rigidly affixed thereto, a driving gear freely rotatable on said shaft, a ratchet carried by the driving gear adapted to engage the ratchet gear, power means for turning the driving gear, a second shaft, a gear train coupling a the shafts operative to turn the second shaft at a slower rate of revolution than the first shaft, a cam on each shaft, a first switch adapted for intermittent actuation by the cam on the first shaft, a second switch adapted for intermittent actuation by'the cam on the second shaft, and

means operative on actuation of the second switch to short-circuit the first switchintermittently at a substantially more rapid rate than the first switch is normally actuated by the cam on the first shaft.

GUSTAVE T. FREDSTROM. REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 767,361 Stephenson, Jr Aug. 9, 1904 1,738,467 Warren Dec. 3, 1929 2,086,715 Jackson July 13, 1937- 2,110,861 Harrison Mar. 15, 1938 

